Spiral Stairs

[Bill Tillman]

I was giving this one a try and it turns out to have some tricks in its geometry. It's going to be cast from concrete and this is what I created thus far.

 

Basically, I drew the inside and outside radii and then started adding risers and connecting points. Once I had that I drew the shape of each end of a tread. Then I lofted between them and copied and aligned the results multiple times for each tread elevation. With my minimal understanding with LOFT this is probably a very crude way of doing it so I thought I'd check if anyone has a better method for constructing this set of stairs.

 

BTW, it does get more complex with a landing on the same radius and then another set of 12 steps before it terminates at the upper floor landing.

Drawing1.dwg

Edited December 3, 2020 by Bill Tillman

[Berzerker]

Being a rookie at AutoCad I think I would have made a solid of the first stair (step) then just copied and pasted them at the right position and elevation (7" X 11") I believe it is.

What are you lofting? I looked at your drawing, great Idea. I might have even created the whole staircase out of a solid and just subtracted the steps from it " Seeimgs how it's being poured out of concrete.

Concrete aint cheap

You can't hide "MONEY".

[Bill Tillman]

As I worked more with this spiral stair rail layout I find out just how much I don't know about the geometry needed to obtain a radiused rail that will also be on a slope of about 37.5° from the horizontal. I would think that of course it could be solved mathematically, but the client I'm working with on this says they never really bother with such detail. Okay, I follow, time is money but my thinking is the material lengths will come up short, for example, there is a channel which runs along the bottom of the handrails and it terminates and begins inside of the vertical posts. It appears in plan view with a 169.5" radius. But then when I tilt it to run up the stairs it's easy to see how its properties will change. ???

Edited December 3, 2020 by Bill Tillman

[BIGAL]

Way back in 1990 did a 3d spiral stair lisp it was a repeat of a single tread including handrail copy vertical and rotated. It was instant done as a sales tool.

 

Any way back to your stair need to add the under side concrete that is what holds them up. Re bottom holds them up "Enzed" stairs are self supporting the treads are oversize each bolted to next so stairs float. Again 1990. 

 

Maybe even add the bottom to your tread then copy and rotate. The tread has a taper inside rad to outside rad. so extrude the shape with correct taper or slice off a over size shape to get taper and curved ends.

 

 

 

[BIGAL]

Now I would use Helix for the hand rail path as it could be drawn in one piece not each tread. I don't think helix existed  back in 1990.

 

If I remember correct  for handrail very easy still for one tread create a 3point ucs point1 is at centre of radius pt2 c/l of handrail, pt3 c/l again has a z of the vertical slope/rise draw an arc on this plane then extrude a shape along arc path.

[Bill Tillman]

Thanks all. I did some searches on this and came up with some good stuff. Mostly seat of the pants stuff with two guys running a length of pipe through a rolling machine while one of them use a pair of vice grips on the back end twisting its axis as it went through the machine. 

 

BIGAL, I'd love to see those formulas and give it a try. I have to submit tomorrow so I'll end up plotting some more points and measure a pline that passes through all of them.

 

And here again is life's little quandary. Wish I could take the time to solve this with a LISP routine but there's no time.

Edited December 3, 2020 by Bill Tillman

[BIGAL]

You should be able to take what I showed as an example for the concrete shape just make yours deeper then should be able to union. Even if ends are square should look ok.

 

Start with a solid shape may be easier than lofted then can be joined. Its a case of insert at new z and rotate.

 

h2 is step height 

ang1 is step plan angle in degs

ip is center of radius so your block insertion point will need to reflect this as you have a large radius.

(setq s2 0)
  (while (< s2 s1)
     (setq ip (list (car ip) (cadr ip) (+ (caddr ip) h2)))
     (command "insert" blkname ip "" "" ang1)
     (setq ang1(+ ang1 22.5))
     (setq s2 (+ s2 1)
   )

Just PM if stuck

 

a quick manual go 1 solid object, unioned 3 together.

 

Edited December 3, 2020 by BIGAL

[BIGAL]

Almost there did not get the bottom angle trim quite right.

 

 

(setq angdiff (/ (- 169.9437000 135.0000000) 12.0))
(setq ang1 135.0)
(setq ip (getpoint "Pick centre"))
(setq h2 6.0)
  (repeat 12
     (setq ip (list (car ip) (cadr ip) (+ (caddr ip) h2)))
     (command "insert" "aaa" ip "" "" ang1)
     (setq ang1(+ ang1 angdiff))
    
   )

 

[Bill Tillman]

Thanks BIGAL, but here's the real problem. This handrail is a monumental one, that is it's not just a round tube. The section through this rail has a bottom channel, a top channel with mesh infill in between these two channels and then a rectangular tube top rail. The shop says they have never made one like this and don't have much info on what they need. BTW, I should say the shop drawings for this are complete but they obviously missed some important points. Like the tread with at the inner radius is almost 3" shorter than the outer radius treads. The stairs are 72" wide so that's what explains the tread width difference. At this point I'm going to have to back up 16 yards and punt.

[SLW210]

You should have access to the AutoCAD Architectural Toolset, it does spiral stairs and rails. It took me only a few hours to figure out how to make a custom rail into a 4 board fence, so customization seems easy.

 

I just did a few simple spiral stairs, seems simple enough.

 

If needed in Autocad you'll need to Convert to 3D Solids.

[Bill Tillman]

While doing some more searches, I found this. Need time to understand what it's doing but looks pretty good for down and dirty detail work.

 

https://www.blocklayer.com/stairs/spiral-stairseng.aspx

 

 

[Dadgad]

16 hours ago, Bill Tillman said:

While doing some more searches, I found this. Need time to understand what it's doing but looks pretty good for down and dirty detail work.

 

https://www.blocklayer.com/stairs/spiral-stairseng.aspx

 

 

That is a great link, bookmarked for future reference, thanks for posting it.

Good luck Bill.